Wearables like smartwatches have been the techie dream since forever. Now it seems as though the dreamm may come true. The mobile revolution has allowed hardware makers to create devices that can fit on your wrist - devices that have the same computing power as devices that used to sit on your desktop.

But while the electronics have shrunk, the batteries haven't, says Marc van den Berg. He's a venture capitalist at Technology Partners in Palo Alto, Calif. On an iPhone, for example, the battery takes up nearly half the real estate of the device.

"If my watch is going to become my new smart phone I don’t want the watch to be a nice piece of jewelry and for me to have to wear a big arm band battery next to it," van den Berg says.

In the past, the battery business wasn't as sexy as the software or mobile hardware biz. But the challenge of powering mobile and wearable devices has sparked a renewed excitement in battery technology among tech companies and investors in Silicon Valley. And it's not just small batteries people are excited about.

"The investment community sees the need -- certainly in consumer electronics - but we also have the automobile marketplace and we have utility scale storage devices," van den Bergsays. "All three of those things are the demand that the investment community has woken up to."

Just down the road from van den Berg, Yi Cui is working in his lab ast Stanford, where he's a professor. He’s also the CEO of a venture backed start-up called Amprius, which tests the boundaries of battery technology. The company counts former Google CEO Eric Schmidt as one of its big name investors.

"My group invented paper batteries and textile battery," he says. And in this lab, Cui also developed a battery that uses silicon, which he sells through Amprius.

Cui says batteries are hard to develop because they live in the world of material science or very simply put, it all depends on finding the right material. Sometimes, materials like paper don’t hold enough charge. Or others like metals, can be too expensive. And often they can be dangerous.

"The safety concern is there. Make sure the packaging is good. You don’t leak out anything bad for your body," he says. Sorting through those issues takes a lot of research, time and testing.

He shows me his battery testing machine. It’s around 4 feet high and has about a 100 little slots. In them, flat silver button batteries, like the ones in a watch. The chip uses silicon, and Cui says it allows the battery to lasts 25 percent longer than other batteries. And Amprius is selling a small number of them to Asian smartphone manufacturers.

Jim Kim is a venture capitalist at Formation 8 and he’s rooting for Amprius.

But, he says, "There’s a valley of death that exists between the research lab and commercialization."

He says while venture capitalists might be funding the research, nobody is paying to manufacture the batteries on a mass scale, at least not in the U.S.

"If you think about what needs to be done, you have to build a plant and that’s very expensive," he says. "And this is a process that takes a long time to tune. You have to be safe with it. If you make a mistake, it’s catastrophic."

Kim says a battery factory can cost up to hundreds of millions of dollars. While the luxury carmaker Tesla wants to build a factory, Kim says it’s mainly Korean conglomerates like LG that are investing, not companies in the U.S.

"And then you’ve had Panasonic, Samsung BYD and Lishen in China, who have built their factories on the back of government subsidies," he says. "Those are the players who are now dominating the market and that’s a shame."